Photographic emulsion



Patented June 15, 1943 PHOTOGRAPHIC' EMULSION Henry C. Yutzy, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. .Y., a corporation of New Jersey No Drawing. Application May 14, 1941, Serial No. 393,413

'7 Claims.

This invention relates to the preparation of gelatin photographic emulsions in which the silver halide is prepared in a solution of a watersoluble ethanolamine cellulose acylate.

One object of my invention is to provide a method of preparing gelatin photographic emulsions which are finer grained than those in which the silver halide is prepared in a solution consisting of gelatin as the solute. Other objects will appear herein.

I have found that if instead of preparing the silver halide to be used in photographic emulsions in gelatin solutions, the precipitations are carried out in solutions of water-soluble ethanolamine cellulose acylates as the dispersing medium, in the preparation of a gelatin emulsion, the resulting gelatin photographic emulsions are finer grained, and differ as to contrast from those emulsions in which gelatin is employed as the dispersing medium in the preparation of the silver halide as Well as the carrier for the silver halide in the emulsion.

This invention may be employed either in preparing gelatin emulsions in which but one silver halide is used or it may be employed for preparing gelatin emulsions in which a mixture of silver halides is used. The silver halide is ordinarily prepared by mixing together an aqueous solution of silver nitrate with an aqueous solution of an alkali metal halide or halides and a dispersing medium. My invention includes any method of preparing silver halide emulsions including gelatin as the carrier in which silver halide therefor is prepared in a solution of a Water-soluble ethanolamine cellulose acylate as the dispersing medium. For instance if a gelatin emulsion is desired containing a mixture of silver halides having diiferent grain sizes, one portion of the silver halide may be prepared in an ethanolamine cellulose acylate dispersing medium While another portion may be prepared in gelatin as the dispersing medium, followed by mixing of the two dispersions and preparation of the photographic emulsion therefrom.

Any of the water-soluble ethanolamine cellulose acylates may be employed as the dispersing medium in preparing silver halide for use in a gelatin photographic emulsion. The acylate groups may be acetyl, propionyl, lactyl or the like or a mixture of acylate groups; the only criterion being that water-soluble derivatives are obtained. Ordinarily the aliphatic acids of not more than 4 carbon atoms are most desirable for this purpose.

ethanolamine cellulose acetate, a di-ethanolamine cellulose acetate, a mixture of these or a compound in which both mono-ethanolamine and di-ethanolamine groups are present; the only criterion being that the compounds are water soluble. The ethanolamine cellulose acetate may be prepared by reacting cellulose acetate, which has been hydrolyzed to a low acetyl content such as 22%, with p-toluene sulfonyl chloride and pyridine to form a cellulose acetate-p-toluene sulionate which is then reacted with an ethanolarnine. The preparation of the ethanolamine cellulose acylates is fully disclosed and is claimed in Kenyon and Reynolds application Serial Number 349,222, filed August 1, 1940.

The method of precipitating the silver halide is not limited to anysingle order of addition of the solutions. For instance if desired aqueous silverenitrate solution may be run with stirring into an aqueous solution of soluble halide and monoor diethanolamine cellulose acetate or silver nitrate solution and halide solution may be run. simultaneously into an agitated solution of monoor diethanolamine cellulose acetate. It is preferred to carry out this precipitation at a pH of approximately 6 and a compatible elevated temperature. The concentrations of the ethanolamines ordinarily useful for preparing silver halides are between /2% and 6%. This proportion may even be exceeded in some cases as the higher concentrations yield the finer grain, other things being equal.

In some cases it may be desirable to use a-mixi ture of an ethanolamine cellulose acetate and gelatin as the dispersing agent in preparing the emulsion, its sensitivity may be increased by digestion or by adding sulfur sensitizer or preferably by both. If desired preliminary to washing or coating the emulsions, larger quantities of gelatin may be added in solution to facilitate setting to a gel. Finishing operations, such as optical sensitization (adding a sensitizing dye) and coating out on to a support such as film base or paper, may be carried out as with ordinary gelatin-silver halide emulsions.

The following examples illustrate the invention: Qne for making a relatively slow, positive type emulsion; the other for making a faster negative emulsion.

Positive type 750 grams of potassium bromide and 30 grams of potassium iodide were dissolved in a solution of 200 grams of diethanolamine cellulose acetate and 6500 cc. of distilled water. The temperature of this solution was brought up 40 C. and if the pH was not approximately six, it was adjusted with either sulfuric acid or ammonia to bring it to that point. 1000 grams of silver nitrate were dissolved in 9000 cc. of distilled water and the temperature was adjusted to 30 C. The silver nitrate solution was added to the other solution With stirring over a ten minute period with the temperature held at 40 C. 1050 grams of dry gelatin was then added and the mass was stirred for 20 minutes at 40 C. The temperature was then lowered so as to cause the emulsion to set. The emulsion was then shredded and Washed in water at 5-8 C. for one hour. It was then melted at 40 C. and one gram of potassium bromide and 500 grams of gelatin were stirred in at 40" until the gelatin was all dissolved. The pH was tested and if not six, was treated as described before so as to attain that value. Distilled water was then added to make the total weight of the batch 60 pounds and it was then finished as any ordinary gelatin-silver halide emulsion. It is to be understood that this and the succeeding example were carried out after the formation of the silver halide in the absence of suificient light to fog the emulsion.

Negative type 750 grams of potassium bromide and 50 grams of potassium iodide were dissolved in a solution of 120 grams of di-ethanolamine cellulose acetate in 6500 cc. of distilled water. The temperature was raised to 40 C. and a pH of six was imparted thereto, using either sulfuric acid or ammonia as necessary. The solution was then heated to bring the temperature to 60 C. 1000 grams of silver nitrate were dissolved in 9000 cc. of distilled water and. the temperature was brought to 55 C. This silver nitrate solution was added to the other solution with stirring over a thirty minute period with the temperature held at 60 C. 1050 grams of dry gelatin was then mixed into the silver halide dispersion and the mass was stirred for 30 minutes, cooling to 50 during this period. The mass was then chilled so as to cause setting of the emulsion. The emulsion was shredded and washed in water at 5-8" C. for one hour. It was then melted at 40 C. and one gram of potassium bromide and 500 grams of gelatin was added thereto and the mass was stirred until the gelatin was dissolved. The pH was adjusted to six and distilled water was added to make the total weight of the mass pounds. The emulsion was then finished in the ordinary manner employed for gelatin-silver halide emulsions.

I claim:

1, A method of preparing a gelatin-silver halide photographic emulsion which comprises preparing the silver halide in a solution of a water-soluble ethanolamine cellulose acylate and subsequently incorporating a sufficient amount of gelatin therein to form a protective colloid for the silver halide.

2. A method of preparing a gelatin-silver halide photographic emulsion which comprises preparing silver halide in a solution of monoethanolamine cellulose acetate and subsequently incorporating suffioient gelatin therein to form a protective colloid for the silver halide.

3. A method of preparing a gelatin-silver halide photographic emulsion which comprises preparing silver halide in a solution of; diethanolamine cellulose acetate and subsequently incorporating sufficient gelatin therein to form a protective colloid for the silver halide.

4. A gelatin-silver halide photographic emulsion essentially consisting of an ethanolamine cellulose acylate, silver halide and gelatin, the silver halide having been formed in an aqueous solution of the ethanolamine cellulose acylate and the gelatin having been subsequently added thereto.

5. A gelatin-silver halide photographic emulsion essentially consisting of an ethanolamine cellulose acetate, silver halide and gelatin, the silver halide having been formed in an aqueous solution of the ethanolamine cellulose acetate and the gelatin having been subsequently added thereto,

6. A gelatin-silver halide photographic emulsion essentially consisting of mono-ethanolamine cellulose acetate, silver halide and gelatin, the silver halide having been formed in an aqueous solution of the ethanolamine cellulose acetate and the gelatin having been subsequently added thereto.

7. A gelatin-silver halide photographic emulsion essentially consisting of diethanolamine cellulose acetate, silver halide and gelatin, the silver halide having been formed in an aqueous solution of the diethanolamine cellulose acetate, and the gelatin having been subsequently added thereto.

HENRY C. YUTZY. 

